The present invention relates to a master cylinder for hydraulic brake systems which is actuatable both by the force applied to a brake pedal exclusively and by an auxiliary force, with a master cylinder piston being slidable by a booster by interposing a hydraulic transmission between the booster and the master cylinder piston.
A master cylinder of this type is shown in German printed patent application DT-OS No. 2,460,529. In this known master cylinder, the hydraulic transmission may be disconnected automatically in the event of failure of the auxiliary force by means of a valve arrangement. When the brake is applied without the auxiliary force, this arrangement makes it possible to generate the braking pressure directly by the relatively small area of the master cylinder so that a sufficiently high braking pressure can still be achieved by making use of the admissible pedal travel. If the auxiliary force were used without the hydraulic transmission interposed between a booster and the master cylinder piston, the maximum possible braking pressure would be limited by the fact that the brake pedal could be stepped down to the stop by the auxiliary force.
A disadvantage of this known master cylinder is that for automatic disconnection of the hydraulic transmission a valve arrangement is required which operates in dependence on the auxiliary force. This makes the master cylinder more expensive. In addition, it increases the danger of failure.